Various non-limiting embodiments disclosed herein generally relate to photochromic materials which comprise a hyperbranched polyester and at least one photochromic group. Other non-limiting embodiments relate to photochromic compositions and articles, such as but not limited to ophthalmic lenses, that include the disclosed photochromic materials.
Photochromic materials can be incorporated into polymeric materials to impart desired optical properties to the polymeric material. For example, photochromic materials have been successfully incorporated into polymeric materials that are used to form ophthalmic lenses, as well as polymeric coatings applied thereto. Typically, the polymeric materials into which the photochromic materials are incorporated are relatively soft, and thus, susceptible to mechanical damage, such as scuffing and scratching. Since it is generally undesirable for certain articles of manufacture, such as ophthalmic lenses, to be susceptible to such damage, often one or more “hard coatings” are applied to the surfaces of the articles to enhance, among other things, their abrasion-resistance. For example, hard coatings are routinely applied to the surfaces of ophthalmic lenses formed from “soft” polymeric materials to enhance their abrasion-resistance.
However, it has been observed that, under certain conditions, photochromic materials have a tendency to migrate from the soft polymeric material into which they are initially incorporated into such other hard coatings. Since the photochromic performance of a photochromic material (i.e., the coloration (or activation) and/or fade rates of the photochromic material) may be influenced by the local environment surrounding the photochromic material, migration may deteriorate photochromic performance. Generally speaking, for an organic photochromic material, the time required for coloration or bleaching to occur tends to increase with the hardness of the local environment surrounding the photochromic material. Thus, when a photochromic material migrates from a relatively soft or flexible environment to a relatively hard or rigid environment, the performance of the material photochromic tends to deteriorate. That is, the time required for coloration and/or bleaching tends to increase. Consequently, migration may result in a decrease of the utility of a photochromic material, as well as that of a coating or an article into which it is incorporated.
One method of reducing the migration of a photochromic material in a polymeric material is to bond the photochromic material to the polymeric material. For example, photochromic materials having relatively short, organic chain segments that can be polymerized into a polymeric material have been disclosed. Such photochromic materials have a reduced tendency to migrate in the polymeric material due to the physical constraints afforded by bonding of the photochromic material to the polymeric material. However, bonding the photochromic material to the polymeric material using such short, organic chain segments can have the effect of slowing the coloration and/or fade rates of the photochromic material as compared to a similar photochromic material that is not bonded to the polymeric material. Additionally, for some photochromic materials, it is preferred to place the short, organic chain segments at locations that are distant from the “active” portion of the photochromic material, i.e., that portion of the photochromic material that undergoes reversible transformation from one state to another on exposure to actinic radiation. That is, for some photochromic materials, if the chain segments are placed too close to the active portion of the photochromic material, the ability of the photochromic material to transform may be impeded. Consequently, the photochromic performance of the material may be diminished.
Other methods of modifying the fade rates of photochromic materials have focused on creating a relatively “soft” environment around the photochromic material, such that the photochromic performance of the material is relatively unaffected by the hardness of the polymeric material into which it is incorporated, rather than reducing migration. For example, photochromic materials that are adducts of a photochromic moiety and at least one pendant oligomeric group have been disclosed. However, because such photochromic materials are not generally bonded to the polymeric materials into which they are incorporated, phase separation may occur if the photochromic materials are not compatible with the polymeric material. That is, the photochromic materials may separate from the polymeric material, which can result in undesirable properties, such as haze and/or blooming, which can limit the utility of the materials in many applications wherein the transparency is important.
Accordingly, it would be advantageous to develop photochromic materials having both a reduced tendency to migrate and favorable coloration and/or fade rates that can be incorporated into a variety of polymeric materials.